The Mercedes-Benz W 108 and W 109 are luxury cars produced by Mercedes-Benz from 1965 through to 1972. They succeeded the W 111 and W 112 "fintail" () sedans, and upon their introduction, the manufacturer designated them as constituting a newly created "Upper Middle Class" range. The cars were successful in West Germany and in export markets including North America and Southeast Asia. During the seven-year run, a total of 383,072 units were manufactured.
As the W 108 and W 109 were only available as 4-door models, the similarly squarish, Paul Bracq-designed 2-door W 111 and W 112 coupés and cabriolets filled those niches and are frequently mistaken for W 108/W 109 two-doors.
Model description
Development and body design
The car's predecessors, the four door W 111 (1959–65) and W 112 (1961–65), helped Mercedes-Benz develop better sales and achieve economy of scale production by unifying the entire Mercedes-Benz range onto a single automobile platform and body, reducing both manufacture time and cost. However, their signature tailfin design on rear fenders, a popular styling feature of the late 1950s quickly went out of fashion in favour of simplicity and practicality (particularly with regard to manufacture and bodyshop repair). After taking over the design school at Mercedes-Benz in 1957, Paul Bracq began steering the styling away from flamboyance to a stronger emphasis on function. The two-door W111 and W112 models introduced in 1961 were the first to show this approach, which saw the fins drastically rounded off. They were, in turn, followed by the W113 Pagoda and the W100 Größer with perfectly square rear fenders. Work on the replacement for the sedan Fintail body began in parallel, and by 1963 the design was finalised. Retaining the W111/W112 platform and underpinnings, the goal was to maximise passenger space while maintaining the favourably compact exterior dimensions of the previous six-cylinder models, to achieve high levels of safety, ride comfort, and performance. In addition, the top-end W112 sedans had very limited demand, looking too similar to the mass-produced downscale four-cylinder W110 (the diesel versions of which were common as taxicabs) - thus the upcoming new sedans should not share underpinnings with lower-tiered models.
While the external dimensions were increased only marginally relative to the preceding Type 220 S — longer, wider, and lower — the interior space efficiency was significantly improved, primarily by dint of curved side windows and a lowered beltline. As a result, interior width increased by in the rear seating area, and by in the front seating area. The floor in front of the rear seats was lowered by , resulting in increased footwell space. The vehicle's centre of gravity was lowered, improving road-holding. The lowered beltline facilitated larger window areas; the windscreen alone was 17 per cent larger than that of the W 111, with total glass area increasing by 12 per cent. The result was a newer-looking, sleeker car with an open and spacious interior. As intended, the flat roof and smooth rear end treatment were stylistically reminiscent of the W111 coupés, W113 roadster and W100 limousine whose sporty and elegant design had garnered worldwide acclaim. The front featured the traditional Mercedes-Benz radiator grille with a wide opening and lowered bonnet and vertical Lichteinheiten lighting units which combined high and low beam headlamps, parking and turn signal lights, and fog lamps into a single, integrated assembly (though U.S. export models used round sealed beam headlamps and separate park/turn lamps in accord with national regulations).
Body construction and paintwork
The body was welded to the chassis floor plate to form a single, torsionally-resistant unit. Vulnerable areas received a seven-layer paint finish consisting of zinc phosphate anti-rust treatment, chromic acid neutralisation, two primer coats, a stone-chip protection coat, undercoat, and topcoat, baked at . The underside, inner fenders, door sills, and front valance were given a thick protective coating of polyvinyl chloride (PVC) weighing approximately 14 kg, which remained elastic to prevent stone damage and provide sound insulation. The engine compartment and underside components were sprayed with a wax coating. Chrome-plated exterior trim comprised five layers over steel: matte copper, polished copper, semi-matte nickel, polished nickel, and a double heavy chrome layer.
Interior design and comfort
The seats were developed in collaboration with medical doctors, using firm cushioning to allow small posture changes and prevent the body from bouncing. The backrest followed the S-shaped curve of the spine, and the bucket-shaped design provided lateral support. The driver's seat offered three-way adjustment: fore-aft, vertical height, and infinitely adjustable backrest angle down to horizontal. Multi-layer insulation separated the engine compartment from the cabin: 18 mm at the bulkhead and over 20 mm on sections of the floor. Ventilation air passed through a dust filter; a three-speed blower operated even when stationary. Air was extracted through slots under the rear window, helping to reduce condensation. Heating was independently adjustable for left and right sides. Luggage capacity was 610 litres. Optional extras included an electrically operated sunroof, electric window lifts, power steering, and air conditioning. Twin high-pitched horns were standard; a third horn was fitted to the later 300 SEL 6.3 and 300 SEL 3.5. From the 1968 model year the interior received new fabric patterns, revised colour schemes, and nylon carpet on the floor and sills.
Model differentiation: W 108 and W 109
Originally, the W 108 was seen as a combined successor to the W 111 and the short-wheelbase sedans in the W 112 line lacking air suspension. In turn, the W 111 was a successor to the six-cylinder Ponton models of the mid-1950s; whilst the W 112, derived from it, was a stopgap to replace the hand-built body-on-frame 300 "Adenauer" (W 189) state car pending the 1963 introduction of the 600 "Grand Mercedes" (W 100; ). In addition to being lavishly decorated with additional chrome trim, the W 112 inherited the alloy block M 189 engine of the W 189, and featured a self-levelling air suspension.
The dividing line between the W 108 and W 109 ran between luxury, performance, and air suspension. The W 109 300 SEL kept the self-levelling air suspension, while the W 108 models from the 300 SEb down retained steel coil springs and a hydropneumatic compensating spring on the rear axle. (A double-acting hydraulic device that used the movements of the swing axle halves to maintain a nearly constant ride height regardless of load). The 300 series were more luxuriously appointed than the 250 series, featuring burled walnut dashboards and fine wood trim. Externally all W 109 models could be distinguished by their door window frames and A-pillars finished with polished metal bright trim. Many optional appointments for the W108 such as power windows, power steering and automatic transmission were standard on the W109, though a fully synchronised manual transmission discount option was available for the latter. Later 3.5 and 6.3 models had a vacuum-controlled central locking system as standard.
Chassis and steering
The front suspension employed a U-profile pressed front axle carrier with double wishbones on each side, separating wheel guidance from springing. Coil springs, gas-filled telescopic shock absorbers, and progressive bump stops were used. A front anti-roll bar was standard; whilst the 300SEL featured an additional rear anti-roll bar. The rear suspension was a single-joint swing axle with a low pivot point; gas-filled shock absorbers prevented oil foaming. The entire suspension was rubber-isolated from the body, and an additional shock absorber on engine mounts damped engine vibrations.
The power steering was a hydraulically assisted recirculating ball design. Below 600 grams of steering wheel force, steering was purely mechanical; above that, a control slide admitted pressurised oil. Road feel was retained, and if assistance failed the car remained fully steerable. The steering system featured a telescopic column, a deformable bushing under the steering wheel, and the steering housing mounted behind the front axle carrier for frontal collision safety.
Air suspension (W 109)
The W 109 300 SEL models were equipped as standard with Daimler-Benz air suspension, developed with Phoenix for the rubber rolling bellows and Bosch for the regulating valves. A compressor drew air through a frost-protection device and delivered it at 16 bar to a reservoir. Three level-control valves (two front, one rear) operated mechanically via rods from the suspension. The driver could select a "high" position via a dashboard switch, raising the body by approximately . The system maintained constant ride height regardless of load, allowing a softer spring rate and optimal toe and camber adjustment.
Safety architecture
In the design of the new body by Béla Barényi the latest findings regarding internal and external occupant protection, based on intensive accident research conducted by Daimler-Benz AG, were incorporated. The structure adhered to the principle of a robust passenger safety cell combined with impact-absorbing crumple zones. The passenger compartment itself was engineered to be exceptionally robust and rigid, while the front and rear sections were designed to be relatively easily deformable to mitigate impact energy.
Internally, a comprehensive suite of passive safety measures was standardised across all models. The instrument panel was embedded within a shock-absorbing frame, and the steering wheel was equipped with a safety hub featuring a large, padded plate. The dashboard was effectively padded along both its top and bottom edges. All pull knobs and door handles were fabricated from elastic materials, and the doors were fitted with special safety locks designed to prevent them from springing open under any circumstances. For exterior protection against minor parking damage, rubber protective strips were integrated into the bumpers, and plastic strips were incorporated into the side trim mouldings.
All models had a dual-circuit power braking system with disc brakes on all four wheels. The parking brake was a small drum inside the rear disc hubs. A brake force regulating valve on the rear wheels allowed larger rear wheel cylinders for stability during light braking while preventing lock-up under heavy braking. The brake booster supplied approximately three-quarters of pedal pressure. From approximately 1969, the regulating valve was eliminated on the sedans in favour of a constant brake pressure distribution, research having shown it equally reliable for the sedan's weight distribution. On the W109 models the rear brake calipers were connected to the chassis via reaction arms to prevent rear-end lift during braking.
First Series (1965–1967)
Market introduction
The W 108/W 109 premiered at the Frankfurt Auto Show in 1965. The initial model range consisted of three W 108s (250 S, 250 SE, and 300 SEb) and a sole W 109 (300 SEL). The inline-six engines were carried over from the previous generation with significant mechanical refinements. The 2.3 L M 127 engine was stroked to 2.5 L while the alloy-block 3.0 L M 189 version was carried over from the W 112.
These models were complemented by the W 111 250 SE coupe and cabriolets, which got the stroked M 129 motor, and the W 112 300 SE which retained the M 189 engine.